Electrophotographic toner

ABSTRACT

This invention relates to a toner for electrophotography which develops an electrostatically charged image, the toner at least containing a coloring agent, a binder resin, a charge control agent, and a functioning agent, wherein low molecular weight polyolefin wax obtained by a metallocene type polymerization catalyst is contained as the function imparting agent. The toner of the invention is excellent in fixability, and has offset preventing properties, heat response characteristic, anti-spent toner properties, and storage stability, which can thus obtain a sharp, high quality image.

TECHNICAL FIELD

The present invention relates to a toner for electrophotography. Morespecifically, this invention relates to a toner in a one-component ortwo-component dry developer, which toner exhibits excellent fixability,offset preventing properties and heat response characteristic at thetime of fixing.

BACKGROUND ART

In recent years, electrophotographic copiers and printers have gainedpopularity because of widespread office automation. With thisbackground, there has been growing demand for electric power saving anddownsizing of the machines in addition to high speed copying.

General formulations for toners in electrophotographic copiers andprinters are shown in Table 1. One of the main factors for improving thefixability and offset preventing properties is a functioning agent, acomponent of the toner. Wax for use during the production of the toner,in particular, affects a binder resin, a principal constituent of thetoner, and proves useful for improving the fixability, offset preventingproperties and heat response characteristic.

That is, an electrophotographic copier or printer feeds a toner to alatent image on a latent image carrier to obtain a visible image, thentransfers the resulting toner image to a plain paper or an OHP film, andfixes the transferred image. Currently, wide varieties of waxes are usedin this field. Among them, low molecular weight polyethylene waxes andlow molecular weight polypropylene waxes are in wide use. The currentmethods of producing polyethylene waxes and polypropylene waxes mainlyemploy Ziegler-Natta catalysts, and are classified into thepolymerization process and the depolymerization process. However, waxesproduced by these methods are defective in that the ratio of the weightaverage molecular weight Mw to the number average molecular weight Mn,the Mw/Mn ratio, exceeds 2, resulting in poor heat responsecharacteristic. This adversely affects the fixability and offsetpreventing properties. Consequently, toners using such waxes cannotfully meet the social demand for saving in electric power and downsizingof the machines in addition to high speed copying.

                                      TABLE 1                                     __________________________________________________________________________                                       (Unit: wt. %)                                               Charge                                                               Binder                                                                            Coloring                                                                           control                                                                           Functioning                                                                         Magnetic                                                                           Electrolytic                                          resin                                                                             agent                                                                              agent                                                                             agent powder                                                                             Solution                                                                            Other                                   __________________________________________________________________________    Two component                                                                         50-100                                                                            0-20 0-10                                                                              0-20  --   --    --                                      system                                                                        One component                                                                          0-100                                                                            0-20 0-10                                                                              0-20  0-60                                               system                                                                        __________________________________________________________________________

The present invention has been accomplished in the light of theaforementioned problems. The object of this invention is to provide atoner in a one-component developer and a two-component developer whichtoner leads to produce a higher grade copy image in anelectrophotographic copier or printer, that is, the toner excellent infixability, offset preventing properties and heat responsecharacteristic.

DISCLOSURE OF THE INVENTION

The present invention provides a toner for electrophotography whichdevelops an electrostatically charged image, the toner at leastcontaining a coloring agent, a binder resin, a charge control agent, anda functioning agent, wherein low molecular weight polyolefin waxobtained by using a metallocene type polymerization catalyst iscontained as the functioning agent.

As a preferred embodiment, the invention also provides the toner forelectrophotography in which the low molecular weight polyolefin wax hasa number average molecular weight, Mn, of 1,000 to 15,000 and a weightaverage molecular weight, Mw, of 1,000 to 30,000 as measured by the GPCmethod, and the Mw/Mn ratio is within the range from 1 to 2. As anotherpreferred embodiment, the invention also provides the toner forelectrophotography in which the low molecular weight polyolefin waxcomprises a polyolefin selected from homopolymers of alpha olefins,copolymers of alpha olefins with other alpha olefins, and copolymers ofalpha olefins with cycloolefins.

To attain the aforementioned object, we, the inventors, have noted thatthe Mw/Mn ratio of polyolefins polymerized commercially usingconventional catalysts exceeds 2, while the Mw/Mn ratio of polyolefinspolymerized using metallocene catalysts can be controlled to be withinthe range from 1 to 2. Thus, we have considered that the use of suchpolyolefins as functioning agents is one of the way improving thefixability, offset preventing properties and heat responsecharacteristic of toner. The present invention has been accomplished onthe basis of such findings. A toner using wax satisfying thesecharacteristics as a functioning agent can affect the binder resin, andserve as a toner for producing a high grade copy image, that is, thetoner which is excellent in fixing strength, offset preventingproperties and heat response characteristic, and which fulfills socialdemand, i.e., saving in electric power, high speed operation, anddownsizing of an electrophotographic copier or printer. The toner of thepresent invention is used as a toner for electrophotography of a heatfixing type, such as a heat roller fixing type. The toner of the rollerfixing type may concurrently have pressure fixing properties. The tonerof the present invention is used in electrophotographic copiers orprinters employing inorganic photosensitive materials or organicphotosensitive materials such as organic photoconductors (OPC).

Details of the present invention will be offered below.

The toner for electrophotography of the present invention ischaracterized in that the functioning agent is low molecular weightpolyolefin wax obtained by using a metallocene type polymerizationcatalyst.

The metallocene type polymerization catalyst as used herein refers to acatalyst system comprising (A) a molecule of a sandwich structure and(B) aluminoxane, the molecule (A) comprising two cyclopentadienyl ringsor substituted cyclopentadienyl rings covalently bonded to a transitionmetal selected from the Groups IVb, Vb and VIb of the periodic table,such as titanium, zirconium, hafnium, vanadium or chromium.

Examples of the low molecular weight polyolefin wax obtained by usingthe metallocene type polymerization catalyst are homopolymers of alphaolefins such as ethylene and propylene, copolymers of alpha olefins withother alpha olefins, and copolymers of alpha olefins with cyclic olefincompounds (e.g. cyclohexene and norbornene).

Preferably, the low molecular weight polyolefin wax has a number averagemolecular weight, Mn, of 1,000 to 15,000 and a weight average molecularweight, Mw, of 1,000 to 30,000 as measured by the GPC method, and itsMw/Mn ratio is within the range from 1 to 2.

The low molecular weight polyolefin wax obtained using the metallocenetype polymerization catalyst is monodisperse as indicated by its verylow Mw/Mn ratio, and involves very small heat of fusion. Thus, the useof this wax is estimated to easily obtain a toner with excellent heatresponse characteristic. This affects the fixing properties of the tonerduring high speed operation, and the offset-free temperature range ofthe toner, thereby contributing to upgrading a copy image and savingelectric power.

The toner of the present invention can be obtained by adding theforegoing functioning agent to a binder resin, a coloring agent and acharge control agent, and if desired, further addition of otheradditives, and processing by known methods such as kneading, grindingand sifting are possibly made. If desired, a flowing agent may befurther added.

As the binder resin there may be used any known ones. Examples includehomopolymers of styrene and its substituted compounds, such aspolystyrene, poly p-chlorostyrene and polyvinyltoluene; styrenecopolymers, such as styrene-p-chlorostyrene copolymer, styrene-propylenecopolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalenecopolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylatecopolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylatecopolymer, styrene-methyl methacrylate copolymer, styrene-ethylmethacrylate copolymer, styrene-butyl methacrylate copolymer,styrene-methyl a-chloromethacrylate copolymer, styrene-acrylonitrilecopolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethylether copolymer, styrene-vinyl methyl ketone copolymer,styrene-butadiene copolymer, styrene-isoprene copolymer,styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer,and styrene-maleic acid ester copolymer; polymethyl methacrylate;polybutyl methacrylate; polyvinyl chloride; polyvinyl acetate;polyethylene; polypropylene; polyesters; polyurethanes; polyamides;epoxy resins; polyvinyl butyral; polyacrylates; rosin; modified rosin;terpene resin; phenolic resins; aliphatic or alicyclic hydrocarbonresins; aromatic petroleum resins; chlorinated paraffin; and paraffinwax. These compounds may be used alone or in combination.

The coloring agent may be a known one, such as carbon black, iron oxidepigment, phthalocyanine blue, phthalocyanine green, rhodamine 6G lake,or Watchung red strontium.

Examples of the charge control agent are known ones such as Nigrosinedyes, fatty acid modified Nigrosine dyes, metallized Nigrosine dyes,metallized fatty acid modified Nigrosine dyes, and chromium complexes of3,5-di-tert-butylsalicylic acid.

To the toner of the present invention, there may be further added aflowing agent such as colloidal silica, aluminum oxide or titaniumoxide, and a lubricant comprising a fatty acid metal salt such as bariumstearate, calcium stearate or barium laurate.

The toner of the invention may be used as a toner for one componentdevelopers or two component developers. Moreover, the toner of theinvention may be used as a one component magnetic toner by incorporatinga magnetic powder, or may be used as a full color toner.

The present invention will be described in more detail by reference toExamples and Comparative Examples.

<Toner preparation method>

Eight % by weight of carbon black (MA-7, Mitsubishi Kagaku), 2% byweight of a charge control agent (Copy Blue RP, Hoechst), 4% by weightof aerosol silica (HDK-H2000, Wacker Chemie), 84% by weight of a binderresin (MC100, Nippon Carbide), and 2% by weight of control wax as afunction imparting agent were mixed, and melt kneaded at 130° C. by atwo roll mill. Then, the mixture was cooled down to solidification, andcrushed, followed by powderizing the particles using a jet mill. Theresulting fine particles were sifted to select particles with an averageparticle diameter of about 10 micrometers, thereby preparing a toner.

EXAMPLE 1

In the above-described toner preparation method, T-516 (a product ofHoechst, a low molecular weight polyolefin resin produced by ametallocene type polymerization catalyst) was used as wax to prepare atoner of Example 1.

EXAMPLE 2

In the above-described toner preparation method, T-668 (a product ofHoechst, a low molecular weight polyolefin resin produced by ametallocene type polymerization catalyst) was used as wax to prepare atoner of Example 2.

EXAMPLE 3

In the above-described toner preparation method, T-692 (a product ofHoechst, a low molecular weight polyolefin resin produced by ametallocene type polymerization catalyst) was used as wax to prepare atoner of Example 3.

EXAMPLE 4

In the above-described toner preparation method, T-246 (a product ofHoechst, a low molecular weight polyolefin resin produced by ametallocene type polymerization catalyst) was used as wax to prepare atoner of Example 4.

COMPARATIVE EXAMPLE 1

In the above-described toner preparation method, polyethylene waxobtained by polymerization using a Ziegler-Natta catalyst (the waxcalled Hoechst Wax PE190, a product of Hoechst) was used as wax toprepare a toner of Comparative Example 1.

COMPARATIVE EXAMPLE 2

In the above-described toner preparation method, polyethylene waxobtained by polymerization using a Ziegler-Natta catalyst (Hoechst WaxPE130, a product of Hoechst) was used as wax to prepare a toner ofComparative Example 2.

COMPARATIVE EXAMPLE 3

In the above-described toner preparation method, depolymerization typepolypropylene wax (Viscol 550P, Sanyo Kasei Kogyo) was used as wax toprepare a toner of Comparative Example 3.

COMPARATIVE EXAMPLE 4

In the above-described toner preparation method, depolymerization typepolypropylene wax (Viscol 660P, Sanyo Kasei Kogyo) was used as wax toprepare a toner of Comparative Example 4.

Table 2 shows the fundamental properties of the polyolefin resinspolymerized by the metallocene catalyst method that were used in thepresent invention.

                                      TABLE 2                                     __________________________________________________________________________        Wt. average                                                                          No. average  Glass                                                     molecular                                                                            molecular                                                                            Degree of                                                                           transition                                            Product                                                                           weight weight dispersion                                                                          temp.                                                 name                                                                              (Mw) (g/mol)                                                                         (Mn) (g/mol)                                                                         Mw/Mn (degrees C.)                                                                        Hue                                             __________________________________________________________________________    T516                                                                              21,000 11,500 1.8   82    Colorless and                                                                 transparent                                     T668                                                                              8,500  4,300  1.9   86    Colorless and                                                                 transparent                                     T692                                                                              9,500  4,700  2.0   75    Colorless and                                                                 transparent                                     T246                                                                              4,500  2,500  1.8   -15   Milky white                                     __________________________________________________________________________

The toners prepared in the Examples and Comparative Examples were eachfed to a commercially available electrophotographic copier (NP9800,Canon Inc., for high speed operation; PC100, Canon Inc., for low speedoperation), and subjected to performance tests. The results are shown inTable 3. Table 3 shows that the toners of the Examples are superior tothe toners of the Comparative Examples in all of the fixability, theoffset preventing properties, and anti-spent toner properties. In termsof storage stability essential for the performance of toner, the tonersof the Examples were free from problems, such as blocking, under thepredetermined conditions, and gave satisfactory results.

                  TABLE 3                                                         ______________________________________                                                  Offset preventing                                                   Fixability  effect                  Anti-spent                                High     Low    Low temp. High temp.                                                                            Storage                                                                             toner                                 speed    speed  region    region  stability                                                                           properties                            ______________________________________                                        Ex. 1 ∘                                                                        Δ                                                                              Δ ∘                                                                         ∘                                                                       ∘                       Ex. 2 ∘                                                                        ∘                                                                        ∘                                                                         ∘                                                                         ∘                                                                       Δ                             Ex. 3 ∘                                                                        ∘                                                                        ∘                                                                         ∘                                                                         ∘                                                                       Δ                             Ex. 4 ∘                                                                        Δ                                                                              Δ ∘                                                                         ∘                                                                       Δ                             Comp. Δ                                                                              x      x       Δ Δ                                                                             x                                   Ex. 1                                                                         Comp. Δ                                                                              x      Δ x       Δ                                                                             x                                   Ex. 2                                                                         Comp. Δ                                                                              x      x       Δ Δ                                                                             x                                   Ex. 3                                                                         Comp. Δ                                                                              x      x       Δ Δ                                                                             x                                   Ex. 4                                                                         ______________________________________                                    

Evaluation methods and evaluation criteria

1)Fixability (in high speed operation and low speed operation)

The toners prepared with the respective formulations were each used forcopying onto recycled papers at a copying rate of 100 copies/min at afixing temperature of 170 to 200° C. for high speed operation, or at acopying rate of 10 copies/min at a fixing temperature of 120 to 140° C.for low speed operation, with the fixing temperature for each copyingcycle being raised by 10° C. The resulting copy samples were rubbed 10times with an eraser by using an abrasion tester of Southerland. Theload during the test was 40 g/Cm². The tested samples were measured forthe printing density using a Macbeth reflection densitometer. The symbolX was assigned when even one of the measured values at the respectivetemperatures was 65% or less. The symbol Δ was assigned when themeasured values at the respective temperatures were 66 to 75%. Thesymbol ◯ was assigned when the measured values at the respectivetemperatures were 76% or more.

2)Offset preventing effect

The toners prepared with the respective formulations were each subjectedto actual copying tests at a copying rate of 100 copies/min at a fixingtemperature of 140 to 240° C. with the fixing temperature for eachcopying cycle being raised by 5° C. The gray scale chart was utilizedfor the tests. A smudge of the fixing roll during the test was evaluatedvisually. Simultaneously, the resulting copied samples were examined bymeans of a Macbeth reflection densitometer. The samples were evaluatedas offset-free when they were free from smudges on the fixing roll andin the non-image areas of copying papers (recycled papers) at therespective temperatures. The symbol ◯ was assigned when the lowtemperature region of the offset-free temperatures (roll temperatures)was lower than 140° C. ; Δ when this low temperature region was 140 to160° C.; and X when this low temperature region was higher than 160° C.The symbol ◯ was assigned when the high temperature region of theoffset-free temperatures (roll temperatures) was higher than 230° C.; Δwhen this high temperature region was 200 to 230° C.; and X when thishigh temperature region was lower than 200° C.

3) Storage stability

The toners prepared with the respective formulations were each storedfor 8 hours under the conditions 60° C. and 50% RH. Then, the storedtoner was sifted through a 100-mesh, whereafter the amount of the tonerremaining on the mesh was divided by the amount of the sample used, andexpressed as a percentage (the result to be hereinafter called meshresidue). When the toner particles agglomerate during storage, thisvalue increases. The main cause of the agglomeration is low meltingsubstances with a melting point of 50° C. or lower that are contained inthe toner composition. The toner with a mesh residue of less than 0.5%was evaluated as ◯, the toner with a mesh residue of 0.5 to 1.0% wasevaluated as Δ, and the toner with a mesh residue of more than 1.0% wasevaluated as X.

4)Anti-spent toner properties

The toners prepared with the respective formulations were each used forcopying. The resulting copy image in the initial stage and the copyimage after copying of 50,000 papers were checked against sample imagesof Data Quest. The ratio of the reflection density of each copy image tothat of the reflection density of the sample image, on the gray scale,was determined by means of a Macbeth reflection densitometer. This ratiowas obtained for both of the image obtained in the initial stage and theimage after 50,000 copies. When both ratios differed by 35% or more, Xwas assigned. For a difference of 34 to 10%, Δ was assigned, and for adifference of 9% or less, ◯ was assigned.

The toner for electrophotography of the present invention contains afunctioning agent which is low molecular weight polyolefin wax obtainedby using a metallocene polymerization catalyst. Thus, this toner hasimprovements in fixability, offset preventing properties, anti-spenttoner properties, and storage stability. Hence, it can contribute tosaving in electricity, downsizing and high speed operation ofelectrophotographic copiers or printers.

What is claimed is:
 1. A toner for electrophotography which develops anelectrostatically charged image, said toner at least containing acoloring agent, a binder resin, a charge control agent, and afunctioning agent, wherein low molecular weight polyolefin wax comprisesco-polymers of alpha olefins with cycloolefins obtained by using ametallocene type polymerization catalyst is contained as saidfunctioning agent.
 2. A toner for electrophotography which develops anelectrostatically charged image, said toner at least containing acoloring agent, a binder resin, a charge controlling agent, a binderresin, a charge control agent, and a functioning agent, wherein lowmolecular weight polyolefin wax comprises copolymers of alpha olefinswith cycloolefins obtained by using a metallocene type polymerizationcatalyst is contained as said functioning agent, andwherein said lowmolecular weight polyolefin wax has a number average molecular weight,Mn, of 1,000 to 15,000 and a weight average molecular weight, Mw, of1,000 to 30,000 as measured by the GPC method, and the MW/Mn ratio iswithin the range from 1 to less than 2.0.
 3. A toner forelectrophotography which develops an electrostatically charged image,said toner at least containing a coloring agent, a binder resin, acharge controlling agent, a binder resin, a charge control agent, and afunctioning agent, wherein low molecular weight polyolefin wax comprisescopolymers of alpha olefins with cycloolefins obtained by using ametallocene type polymerization catalyst is contained as saidfunctioning agent, and wherein said low molecular weight polyolefin waxhas a number average molecular weight, Mn, of 1,000 to 15,000 and aweight average molecular weight, Mw, of 1,000 to 30,000 as measured bythe GPC method, and the MW/Mn ratio is within the range from 1 to 1.9.